Water Quality

Water quality indicators are divided into four categories, each of which has been identified by the program as a priority area of concern. The categories include hypoxia (low dissolved oxygen) and nutrients; toxic contaminants; pathogens; and floatable debris. These indicators help resource managers assess recent and historical water quality trends, and management efforts to improve conditions.

Chlorophyll a is the green pigment in plants, and the concentration in surface water is an indicator of the amount of microscopic plants (called phytoplankton). This indicator is intended to characterize the spring phytoplankton bloom conditions in the western Sound each year.
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Hypoxia is a condition that occurs in bodies of water as dissolved oxygen concentrations decrease to levels where organisms become physically stressed and ultimately cannot survive. Duration of hypoxia refers to the number of days in a year during which hypoxia was observed in Long Island Sound.
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Hypoxia is a condition that occurs in bodies of water as dissolved oxygen concentrations decrease to levels where organisms become physically stressed and ultimately cannot survive. The area of hypoxia in Long Island Sound refers to the number of square miles in which dissolved oxygen concentrations were less than 3 mg/L over the course of a single year.
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Beaches are closed when high abundances of pathogens (bacteria or viruses) are detected or when heavy rainfall results in a high risk of increased pathogens. A large number of beach closure days can be an indicator of a problem with pathogen contamination or of an unusually wet year.
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WQ Historical/Legacy

Areas designated as "no discharge zones" prohibit the release of sewage from any vessels. Sewage can damage habitats and be a major source of pathogens to the coastal environment. This map shows the areas in Long Island Sound designated as No Discharge Zones.
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Sediment cores were sampled near Norwalk Harbor to determine the historic trends of toxic contamination in the seafloor sediment of the Sound. The cores give a record of metal contamination from the pre-colonial period to the post-industrial era.
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Clostridium perfringens, a bacterial spore found in sediments, is an indicator of sewage inputs and can be used to create a historical record of the magnitude of sewage input to the Sound.
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